Erecting equal-magnification lens array plate, optical scanning unit, image reading device, and image writing device

ABSTRACT

An erecting equal-magnification lens array plate includes: a first lens array plate provided with a plurality of first lenses arranged on a first surface and a plurality of second lenses arranged on a second surface; and a second lens array plate provided with a plurality of third lenses arranged on a third surface and a plurality of fourth lenses arranged on a fourth surface. The first and second lens array plates are stacked. An intermediate light-shielding member provided with a plurality of intermediate through holes is between the first lens array plate and the second lens array plate. The intermediate through hole is formed such that the hole diameter is progressively smaller in a tapered fashion away from the second surface toward the third surface. A plurality of V grooves are formed in an area between adjacent second lenses on the second surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an erecting equal-magnification lensarray plate used in image reading devices and image writing devices.

2. Description of the Related Art

Some image reading devices such as scanners are known to use erectingequal-magnification optics. Erecting equal-magnification optics arecapable of reducing the size of devices better than reduction optics. Inthe case of image reading devices, an erecting equal-magnificationoptical system comprises a linear light source, an erectingequal-magnification lens array, and a linear image sensor.

A rod lens array capable of forming an erect equal-magnification imageis used as an erecting equal-magnification lens array in an erectingequal-magnification optical system. Normally, a rod lens array comprisesan arrangement of rod lenses in the longitudinal direction (mainscanning direction of the image reading device) of the lens array. Byincreasing the number of rows of rod lenses, the proportion of lighttransmitted is improved and unevenness in the amount of lighttransmitted is reduced. Due to cost concerns, it is common to use one ortwo rows of rod lenses in an array.

Meanwhile, an erecting equal-magnification lens array plate could beformed as a stack of two transparent lens array plates built such thatthe optical axes of individual convex lenses are aligned, where eachtransparent lens array plate includes a systematic arrangement ofmicro-convex lenses on both surfaces of the plate. Since an erectingequal-magnification lens array plate such as this can be formed by, forexample, injection molding, an erecting equal-magnification lens arraycan be manufactured at a relatively low cost.

An erecting equal-magnification lens array plate lacks a wall for rayseparation between adjacent lenses. Therefore, there is a problem inthat a light ray diagonally incident on an erecting equal-magnificationlens array plate travels diagonally inside the plate and enters anadjacent convex lens, creating noise (referred to as ghost noise) as itleaves the plate.

There is known an erecting equal-magnification lens array plate in whicha light-shielding member is provided between the two lens array platesin order to reduce ghost noise (see, for example, patent document No.1).

-   [patent document No. 1] JP2009-069801

As described in patent document 1, ghost noise can be reduced to acertain extent merely by providing a light-shielding member between thetwo lens array plates. In order to form an erect equal-magnificationimage with higher quality, however, it is desirable to further reduceghost noise.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned disadvantage and apurpose thereof is to provide an erecting equal-magnification lens arrayplate capable of improving the performance of reducing ghost noise andto provide an optical scanning unit, an image reading device, and animage writing device in which the erecting equal-magnification lensarray plate is used.

To address the aforementioned problem, the erecting equal-magnificationlens array plate according to an embodiment of the present inventioncomprises: a first lens array plate provided with a plurality of firstlenses systematically arranged on a first surface and a plurality ofsecond lenses systematically arranged on a second surface opposite tothe first surface; and a second lens array plate provided with aplurality of third lenses systematically arranged on a third surface anda plurality of fourth lenses systematically arranged on a fourth surfaceopposite to the third surface, wherein the first lens array plate andthe second lens array plate form a stack such that the second surfaceand the third surface face each other to ensure that a combination ofthe lenses aligned with each other form a coaxial lens system, and anerect equal-magnification image of an object on the first surface sideis formed on an image plane facing the fourth surface. The erectingequal-magnification lens array plate further comprises an intermediatelight-shielding member provided with a plurality of intermediate throughholes corresponding to the second and third lenses and provided betweenthe first lens array plate and the second lens array plate such that theintermediate through holes are located directly opposite to thecorresponding second and third lenses. A plurality of V grooves areformed in an area between adjacent second lenses on the second surfaceand/or an area between adjacent third lenses on the third surface.

Another embodiment of the present invention also relates to an erectingequal-magnification lens array plate. The erecting equal-magnificationlens array plate comprises: a first lens array plate provided with aplurality of first lenses systematically arranged on a first surface anda plurality of second lenses systematically arranged on a second surfaceopposite to the first surface; and a second lens array plate providedwith a plurality of third lenses systematically arranged on a thirdsurface and a plurality of fourth lenses systematically arranged on afourth surface opposite to the third surface, wherein the first lensarray plate and the second lens array plate form a stack such that thesecond surface and the third surface face each other to ensure that acombination of the lenses aligned with each other form a coaxial lenssystem, and an erect equal-magnification image of an object on the firstsurface side is formed on an image plane facing the fourth surface. Theerecting equal-magnification lens array plate further comprises anintermediate light-shielding member provided with a plurality ofintermediate through holes corresponding to the second and third lensesand provided between the first lens array plate and the second lensarray plate such that the intermediate through holes are locateddirectly opposite to the corresponding second and third lenses. Theintermediate through hole is formed such that the hole diameter isprogressively smaller in a tapered fashion away from the second surfacetoward the third surface. A plurality of V grooves are formed in an areabetween adjacent second lenses on the second surface.

Still another embodiment of the present invention also relates to anerecting equal-magnification lens array plate. The erectingequal-magnification lens array plate comprises: a first lens array plateprovided with a plurality of first lenses systematically arranged on afirst surface and a plurality of second lenses systematically arrangedon a second surface opposite to the first surface; and a second lensarray plate provided with a plurality of third lenses systematicallyarranged on a third surface and a plurality of fourth lensessystematically arranged on a fourth surface opposite to the thirdsurface, wherein the first lens array plate and the second lens arrayplate form a stack such that the second surface and the third surfaceface each other to ensure that a combination of the lenses aligned witheach other form a coaxial lens system, and an erect equal-magnificationimage of an object on the first surface side is formed on an image planefacing the fourth surface. The erecting equal-magnification lens arrayplate further comprises an intermediate light-shielding member providedwith a plurality of intermediate through holes corresponding to thesecond and third lenses and provided between the first lens array plateand the second lens array plate such that the intermediate through holesare located directly opposite to the corresponding second and thirdlenses. The intermediate through hole is formed such that the holediameter is progressively larger in an inversely tapered fashion awayfrom the second surface toward the third surface. A plurality of Vgrooves are formed in an area between adjacent third lenses on the thirdsurface.

The V grooves may be formed to extend substantially parallel to the mainscanning direction of the erecting equal-magnification lens array plate.The total width of the V grooves in the sub-scanning direction is equalto or more than an aperture size of the first lenses. The adjacent Vgrooves are contiguous with each other at their ends in the sub-scanningdirection.

Yet another embodiment of the present invention relates to an opticalscanning unit. The optical scanning unit comprises: a linear lightsource configured to illuminate an original to be read; theaforementioned erecting equal-magnification lens array plate configuredto condense light reflected by the original to be read; and a linearimage sensor configured to receive light transmitted by the erectingequal-magnification lens array plate.

Still another embodiment of the present invention relates to an imagereading device. The image reading device comprises: the aforementionedoptical scanning unit; and an image processing unit configured toprocess an image signal detected by the optical scanning unit.

Yet another embodiment of the present invention relates to an imagewriting device. The image writing device comprises: an LED arraycomprising an array of a plurality of LED's; the aforementioned erectingequal-magnification lens array plate for condensing light emitted fromthe LED array; and a photosensitive drum for receiving the lighttransmitted through the erecting equal-magnification lens array plate.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses,and systems may also be practiced as additional modes of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 shows an image reading device according to an embodiment of thepresent invention;

FIG. 2 shows a cross section of the optical scanning unit in the mainscanning direction;

FIG. 3 shows a cross section of the erecting equal-magnification lensarray plate along A-A in FIG. 2;

FIG. 4 is a front view of the second surface of the first lens arrayplate;

FIG. 5 shows a cross section of the erecting equal-magnification lensarray plate according to the comparative embodiment in the main scanningdirection;

FIG. 6 shows a cross section of the erecting equal-magnification lensarray plate according to the comparative embodiment in the sub-scanningdirection;

FIG. 7 shows the operation of the erecting equal-magnification lensarray plate according to the embodiment;

FIG. 8 shows the erecting equal-magnification lens array plate accordingto an alternative embodiment of the present invention;

FIG. 9 shows a relationship between the angle of inclination of theslope of the V groove in the second surface and the angle of raydeflection;

FIG. 10 shows an optical path occurring when the angle of inclination εof the slope of the V groove in the second surface is equal to or lessthan the critical angle θc;

FIG. 11 shows an optical path occurring when the angle of inclination εof the slope of the V groove in the second surface is more than thecritical angle θc;

FIG. 12 shows a relationship between the angle of inclination ε of theslope of the V groove in the second surface and the angle of raydeflection γ;

FIG. 13 shows a relationship between the angle of inclination ε of theslope of the V groove in the third surface and the angle of raydeflection γ;

FIG. 14 shows the erecting equal-magnification lens array plateaccording to a second alternative embodiment of the present invention;

FIG. 15 shows the erecting equal-magnification lens array plateaccording to the exemplary embodiment of the present invention;

FIG. 16 shows a result of simulation in the comparative exemplaryembodiment and the exemplary embodiment; and

FIG. 17 shows the image writing device according to another embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

FIG. 1 shows an image reading device 100 according to an embodiment ofthe present invention. As shown in FIG. 1, the image reading device 100comprises a housing 102, a glass plate 14 on which a document G isplaced, an optical scanning unit 10 accommodated in the housing 102, adriving mechanism (not shown) for driving the optical scanning unit 10,and an image processing unit (not shown) for processing data read by theoptical scanning unit 10.

The optical scanning unit 10 comprises a linear light source 16 forilluminating a document G placed on a glass plate 14, an erectingequal-magnification lens array plate 11 for condensing light reflectedfrom the document G, a linear image sensor (photoelectric transducer) 20for receiving light condensed by the erecting equal-magnification lensarray plate 11, and a case (not shown) for fixing the linear lightsource 16, the erecting equal-magnification lens array plate 11, and thelinear image sensor 20.

The linear light source 16 is a light source emitting a substantiallystraight light. The linear light source 16 is secured such that theoptical axis thereof passes through the intersection of the optical axisAx of the erecting equal-magnification lens array plate 11 and the topsurface of the glass plate 14. The light exiting from the linear lightsource 16 illuminates the document G placed on the glass plate 14. Thelight illuminating the document G is reflected by the document G towardthe erecting equal-magnification lens array plate 11.

The erecting equal-magnification lens array plate 11 comprises a stackof a first lens array plate 24 and a second lens array plate 26 builtsuch that pairs of corresponding lenses form a coaxial lens system,where each lens array plate is formed with a plurality of convex lenseson both surfaces of the plate, as described later. The first lens arrayplate 24 and the second lens array plate 26 are held by a holder (notshown) in a stacked state. The erecting equal-magnification lens arrayplate 11 is installed in the image reading device 100 such that thelongitudinal direction thereof is aligned with the main scanningdirection and the lateral direction thereof is aligned with thesub-scanning direction.

The erecting equal-magnification lens array plate 11 is configured toreceive linear light reflected from the document G located above andform an erect equal-magnification image on an image plane located below,i.e., a light-receiving surface of the linear image sensor 20. The imagereading device 100 can read the document G by scanning document G withthe optical scanning unit 10 in the sub-scanning direction.

FIG. 2 shows a cross section of the optical scanning unit 10 in the mainscanning direction. Referring to FIG. 2, the vertical direction in theillustration represents main scanning direction (longitudinal direction)of the erecting equal-magnification lens array plate 11 and the depthdirection in the illustration represents the sub-scanning direction(lateral direction).

As described above, the erecting equal-magnification lens array plate 11comprises a stack of the first lens array plate 24 and the second lensarray plate 26. Each of the first lens array plate 24 and the secondlens array plate 26 is a rectangular plate and is provided with anarrangement of a plurality of convex lenses on both sides thereof.

The first lens array plate 24 and the second lens array plate 26 areformed by injection molding. Preferably, each of the first lens arrayplate 24 and the second lens array plate 26 is formed of a materialamenable to injection molding, having high light transmittance in adesired wavelength range, and having low water absorption. Desiredmaterials include cycloolefin resins, olefin resins, norbornene resins,and polycarbonate.

A plurality of first lenses 24 a are arranged in a single line on afirst surface 24 c (one of the surfaces of the first lens array plate24) in the longitudinal direction of the first lens array plate 24. Aplurality of second lenses 24 b are arranged in a single line on asecond surface 24 d of the first lens array plate 24 opposite to thefirst surface 24 c in the longitudinal direction of the first lens arrayplate 24. As shown in FIG. 2, the lens diameter of the second lenses 24b is smaller than the lens diameter of the first lenses 24 a in thisembodiment.

A plurality of third lenses 26 a are arranged in a single line on athird surface 26 c (one of the surfaces of the second lens array plate26) in the longitudinal direction of the second lens array plate 26. Aplurality of fourth lenses 26 b are arranged in a single line on afourth surface 26 d opposite to the third surface 26 c in thelongitudinal direction of the second lens array plate 26. As shown inFIG. 2, the lens diameter of the third lenses 26 a is smaller than thelens diameter of the fourth lenses 26 b in this embodiment. The lensdiameter of the third lenses 26 a is equal to the lens diameter of thesecond lenses 24 b, and the lens diameter of the fourth lenses 26 b isequal to the lens diameter of the first lenses 24 a.

In this embodiment, it is assumed that the first lens 24 a, the secondlens 24 b, the third lens 26 a, and the fourth lens 26 b are sphericalin shape. Alternatively, the lenses may have aspherical shapes.

The first lens array plate 24 and the second lens array plate 26 form astack such that the second surface 24 d and the third surface 26 c faceeach other to ensure that a combination of the first lens 24 a, thesecond lens 24 b, the third lens 26 a, and the fourth lens 26 b alignedwith each other form a coaxial lens system. In other words, the firstand second lens array plates 24 and 26 form a stack such that theoptical axes of the first, second, third, and fourth lenses 24 a, 24 b,26 a, and 26 b aligned with each other are aligned.

A first surface light-shielding member 30 is provided on the firstsurface 24 c of the first lens array plate 24. The first surfacelight-shielding member 30 is a member of a film form made of alight-shielding material and is formed with a plurality of first surfacethrough holes 30 a. The first surface through holes 30 a are arranged ina single line in the longitudinal direction of the first surfacelight-shielding member 30 so as to be in alignment with the first lenses24 a of the first lens array plate 24. The hole diameter of the firstsurface through hole 30 a is equal to the effective diameter of thefirst lens 24 a. The first surface light-shielding member 30 is providedon the first surface 24 c such that each first surface through hole 30 ais located directly opposite to the corresponding first lens 24 a. Inother words, the first surface light-shielding member 30 is provided onthe first surface 24 c such that the central axis of each first surfacethrough hole 30 a is aligned with the optical axis of the correspondingfirst lens 24 a. As shown in FIG. 2, an area 24 e (hereinafter, alsoreferred to as “first surface flat area 24 e”) on the first surface 24 coutside the effective region of the first lenses 24 a is covered by thefirst surface light-shielding member 30. The term “effective region of alens” refers to a portion having the function of a lens. The firstsurface light-shielding member 30 shields light not contributing toimaging. The first surface light-shielding member 30 may be formed byprinting the first surface 24 c with a light-shielding pattern using alight-absorbing material such as black ink.

A fourth surface light-shielding member 32 is provided on the fourthsurface 26 d of the second lens array plate 26. The fourth surfacelight-shielding member 32 is a member of a plate form made of alight-shielding material and is formed with a plurality of fourthsurface through holes 32 a. The fourth surface through holes 32 a arearranged in a single line in the longitudinal direction of the fourthsurface light-shielding member 32 so as to be in alignment with thefourth lenses 26 b of the second lens array plate 26. The fourth surfacethrough hole 32 a is cylindrically formed and the hole diameter thereofis equal to the effective diameter of the fourth lens 26 b. The fourthsurface light-shielding member 32 is provided on the fourth surface 26 dsuch that each fourth surface through hole 32 a is located directlyopposite to the corresponding fourth lens 26 b. In other words, thefourth surface light-shielding member 32 is provided on the fourthsurface 26 d such that the central axis of each fourth surface throughhole 32 a is aligned with the optical axis of the corresponding fourthlens 26 b. As shown in FIG. 2, an area 26 e (hereinafter, also referredto as “fourth surface flat area 26 e”) on the fourth surface 26 doutside the effective region of the fourth lenses 26 b is covered by thefourth surface light-shielding member 32.

Preferably, the fourth surface light-shielding member 32 may be formedby, for example, injection molding, using a light absorbing materialsuch as black ABS resin. Alternatively, the fourth surfacelight-shielding member 32 may be formed by stacking a black resin paint.

In this specification, the first surface light-shielding member 30 isconfigured in a “film form” and the fourth surface light-shieldingmember 32 is configured in a “plate form”. This means that the firstsurface light-shielding member 30 is far thinner than the fourth surfacelight-shielding member 32. In other words, the term “film form” meansthat the thickness is negligibly small.

As shown in FIG. 2, an intermediate light-shielding member 34 isprovided between the first lens array plate 24 and the second lens arrayplate 26. The intermediate light-shielding member 34 is a member of aplate form made of a light-shielding material and is formed with aplurality of intermediate through holes 34 a. The intermediate throughholes 34 a are arranged in a single line in the longitudinal directionof the intermediate light-shielding member 34 so as to be in alignmentwith the second lenses 24 b and the third lenses 26 a. In thisembodiment, the intermediate through hole 34 a is formed as a circulartruncated cone such that the hole diameter is progressively smaller in atapered fashion away from the second surface 24 d toward the thirdsurface 26 c. The intermediate light-shielding member 34 is providedbetween the first lens array plate 24 and the second lens array plate 26such that each intermediate through hole 34 a is located directlyopposite to the corresponding second lens 24 b and the third lens 26 a.In other words, the intermediate light-shielding member 34 is providedbetween the first lens array plate 24 and the second lens array plate 26such that the central axis of each intermediate through hole 34 a isaligned with the optical axis of the corresponding second lens 24 b andthird lens 26 a.

As shown in FIG. 2, the second surface inter-lens area 24 f and thethird surface inter-lens area 26 f are covered by the intermediatelight-shielding member 34. As described above, the intermediate throughhole 34 a of the intermediate light-shielding member 34 is formed as acircular truncated cone such that the hole diameter is progressivelysmaller in a tapered fashion away from the second surface 24 d towardthe third surface 26 c. Therefore, the third surface inter-lens area 26f is completely covered by the intermediate light-shielding member 34,but the second surface inter-lens area 24 f is not completely covered bythe intermediate light-shielding member 34. A part of the second surfaceinter-lens area 24 f is exposed.

For example, the intermediate light-shielding member 34 may be formedby, for example, injection molding, using a light absorbing materialsuch as black ABS resin. Alternatively, the intermediate light-shieldingmember 34 may be formed by stacking a black resin paint.

The intermediate through hole 34 a is formed as a circular truncatedcone in order to reduce flare noise. The intermediate light-shieldingmember 34 has the function of reducing ghost noise by shielding raysdiagonally traveling in the first lens array plate 24. However, the rayincident on the interior wall surface of the intermediate through hole34 a is not completely absorbed even if a light absorbing material isused. The ray is partly reflected by the interior wall surface (Fresnelreflection).

If the intermediate through hole of the intermediate light-shieldingmember 34 is formed as a cylinder instead of a circular truncated coneas in this embodiment, the ray reflected by the interior wall of theintermediate through hole might be incident on the linear image sensor20 after being transmitted through the second lens array plate 26,creating flare noise.

FIG. 2 shows an optical path of a ray L (chain line) emitted from apoint on the document G, in order to illustrate how flare noise isremoved in the erecting equal-magnification lens array plate 11according to this embodiment. In this embodiment, the intermediatethrough hole 34 a is formed as a circular truncated cone such that thehole diameter is progressively smaller in a tapered fashion away fromthe second surface 24 d toward the third surface 26 c. In other words,the interior wall surface of the intermediate through hole 34 a isinclined with respect to the optical axis Ax of the lens. Due to theinclination of the interior wall surface, the angle of reflection of theray at the interior wall surface of the intermediate through hole 34 ais smaller than when the intermediate through hole is formed as acylinder. The angle of reflection is defined as an angle formed by thenormal to the interior wall surface and the reflected ray. Denoting theangle of inclination of the interior wall surface with respect to theoptical axis Ax by θ, it is ensured that the angle of reflection of theray L is smaller by 2θ than the angle of reflection occurring when theintermediate through hole is formed as a cylinder by tapering theinterior wall surface by θ with respect to the optical axis Ax. Due tothe smaller angle of reflection, the ray L impinges on the fourthsurface light-shielding member 32 and so is shielded or at leastattenuated. Therefore, according to this embodiment, the ray L1 does notsubstantially reach the linear image sensor 20 so that flare noise isprevented.

FIG. 3 is a cross section of the erecting equal-magnification lens arrayplate 11 along A-A in FIG. 2. Referring to FIG. 3, the verticaldirection in the illustration represents sub-scanning direction (lateraldirection) of the erecting equal-magnification lens array plate 11 andthe depth direction in the illustration represents the main scanningdirection (longitudinal direction). FIG. 4 is a front view of the secondsurface 24 d of the first lens array plate 24. The feature of theerecting equal-magnification lens array plate 11 according to theembodiment is found in an area 24 f (hereinafter, “second surfaceinter-lens area 24 f”) between adjacent second lenses 24 b on the secondsurface 24 d of the first lens array plate 24. Therefore, the A-A lineof FIG. 2 is drawn such that a part thereof passes through the secondsurface inter-lens area 24 f. In the embodiment, an area 26 f(hereinafter, “third surface inter-lens area 26 f”) between adjacentthird lenses 26 a on the third surface 26 c of the second lens arrayplate 26 is formed as a flat surface.

As shown in FIGS. 3 and 4, the second surface inter-lens area 24 f isformed with a plurality of V grooves 40 in the embodiment. The V grooves40 have a function of deflecting light incident on the second surfaceinter-lens area 24 f in the sub-scanning direction of the erectingequal-magnification lens array plate 11. The direction of deflection canbe controlled by changing the angle of inclination of the slope of the Vgrooves 40.

As shown in FIGS. 3 and 4, the plurality of V grooves 40 are formed toextend substantially parallel to the main scanning direction of theerecting equal-magnification lens array plate 11. The V grooves 40 arearranged such that adjacent V grooves are contiguous with each other attheir ends in the sub-scanning direction. The V grooves 40 may beprovided by forming the second surface 24 d with concave portions havinga triangular cross section or forming the second surface 24 d withconvex portions having a triangular cross section.

The erecting equal-magnification lens array plate 11 as configured aboveis built in the image reading device 100 such that the distance from thefirst lens 24 a to the document G and the distance from the fourth lens26 b to the linear image sensor 20 are equal to a predetermined workingdistance.

A description will now be given of the operation of the erectingequal-magnification lens array plate 11 according to the embodiment.Before describing the operation of the erecting equal-magnification lensarray plate 11, a comparative embodiment will be shown.

FIG. 5 shows a cross section of an erecting equal-magnification lensarray plate 611 according to a comparative embodiment in the mainscanning direction. In the erecting equal-magnification lens array plate611 according to the comparative embodiment, the second surfaceinter-lens area 24 f is formed as a flat surface. The other aspects areidentical to those of the erecting equal-magnification lens array plate11 according to the embodiment shown in FIG. 2.

FIG. 5 shows optical paths of a ray L1 (solid line), a ray L2 (brokenline), and a ray L3 (chain line) emitted from the document G. The raysL1-L3 are diagonally incident on the erecting equal-magnification lensarray plate 611.

Much of the ray diagonally incident on the erecting equal-magnificationlens array plate 611 is absorbed or at least attenuated by theintermediate light-shielding member 34, as represented by the ray L1.However, since a part of the second surface inter-lens area 24 f isexposed, the rays such as the rays L2 and L3 transmitted through theexposed portion may not be shielded by the intermediate light-shieldingmember 34 or the fourth surface light-shielding member 32 and reach thelinear image sensor 20, creating ghost noise. The rays L2 and L3originate ghost noise and so are stray light.

FIG. 6 shows a cross section of the erecting equal-magnification lensarray plate 611 according to the comparative embodiment in thesub-scanning direction. FIG. 6 shows optical paths of a ray L4 (brokenline) and a ray L5 (chain line). L4 and L5 in FIG. 6 represent theextent of the rays L2 and L3 in FIG. 5 in the sub-scanning direction andrepresent stray light that leave the document G, pass through the firstand second lens array plates 24 and 26, and reach the linear imagesensor 20. As known from FIGS. 5 and 6, the erecting equal-magnificationlens array plate 611 according to the comparative embodiment producesstray light that cannot be shielded merely by providing the intermediatelight-shielding member 34.

FIG. 7 shows the operation of the erecting equal-magnification lensarray plate 11 according to the embodiment. FIG. 7 is a cross section ofthe erecting equal-magnification lens array plate 11 along A-A in FIG.2. As in FIG. 6, FIG. 7 also shows optical paths of the ray L4 (brokenline) and the ray L5 (chain line).

As shown in FIG. 7, the erecting equal-magnification lens array plate 11according to the embodiment is configured such that the rays L4 and L5are deflected in the sub-scanning direction of the erectingequal-magnification lens array plate 11 by the V grooves 40 formed inthe second surface inter-lens area 24 f. The rays L4 and L5 deflected bythe V grooves 40 are absorbed or at least attenuated by the intermediatelight-shielding member 34 and so do not reach the linear image sensor20. In other words, according to the erecting equal-magnification lensarray plate 11 of the embodiment, stray light that cannot be shielded inthe erecting equal-magnification lens array plate 611 according to thecomparative embodiment can be shielded. Consequently, an erectequal-magnification image with higher quality in which ghost noise isreduced more successfully than the erecting equal-magnification lensarray plate 611 according to the comparative embodiment can be formed.

As shown in FIG. 6, the optical path of the stray light originatingghost noise is similar to that of the imaging light except that thestray light passes through the second surface inter-lens area 24 f andthe third surface inter-lens area 26 f. Therefore, the width of thesecond surface inter-lens area 24 f in the sub-scanning directionthrough which the stray light could pass does not exceed the aperturesize of the first lens 24 a. Accordingly, as shown in FIG. 3, the widthW1 of the V grooves 40 in the sub-scanning direction need only be equalto or more than the aperture size D1 of the first lens 24 a. Theaperture size D1 of the first lens 24 a is equal to the hole diameter ofthe first surface through hole 30 a of the first surface light-shieldingmember 30.

The V grooves need be provided in an inter-lens area located on the sidewhere the hole diameter of the intermediate through hole 34 a is larger(the second surface inter-lens area 24 f in the case of the embodiment).If the intermediate light-shielding member 34 is displaced from where itshould be during manufacturing, the third surface inter-lens area 26 fof the third surface 26 c, where no V grooves are provided, is notcompletely covered by the intermediate light-shielding member 34,exposing a flat surface. This might create ghost noise. For this reason,it is desirable that the V grooves be formed both in the second surface24 d and the third surface 26 c.

FIG. 8 shows an erecting equal-magnification lens array plate 1011according to an alternative embodiment of the present invention. As inFIG. 6, FIG. 8 shows optical paths of the ray L4 (broken line) and theray L5 (chain line). The erecting equal-magnification lens array plate1011 according to the alternative embodiment is configured such that theV grooves 40 are formed to cause the ray incident on the second surfaceinter-lens area 24 f to be reflected toward the first surface 24 c. Byadjusting the angle of inclination of the slope of the V grooves 40, therays L4 and L5 incident on the second surface inter-lens area 24 f canbe reflected toward the first surface 24 c. According to the alternativeembodiment, stray light that cannot be shielded in the erectingequal-magnification lens array plate 611 according to the comparativeembodiment can be shielded. Consequently, an erect equal-magnificationimage with higher quality in which ghost noise is reduced moresuccessfully than the erecting equal-magnification lens array plate 611according to the comparative embodiment can be formed. In furtheraccordance with the alternative embodiment, the stray light can bedirected in a direction opposite to the linear image sensor 20.Therefore, the stray light is more properly prevented from beingincident on the linear image sensor 20 so that ghost noise is moresuccessfully reduced.

FIG. 9 shows a relationship between the angle of inclination of theslope of the V grooves in the second surface and the angle of raydeflection. A discussion will be given of how a ray L6 (broken line)incident on the V groove 40, which is formed to have an isoscelestriangle cross section, at an angle of 0° is deflected. The ray havingan angle of incidence of 0° means a ray perpendicularly incident on theerecting equal-magnification lens array plate. As shown in FIG. 9, theangle formed by the slope of the V groove 40 and the surface parallel tothe first lens array plate 24 will be defined as an angle of inclinationε. The V groove 40 shown in FIG. 9 is formed such that the angle ofinclination ε of one of the slopes 40 a is equal to the angle ofinclination ε of the other slope 40 b. The angle formed by the lineperpendicular to the first lens array plate 24 and the ray L6 leavingthe slope of the V groove 40 will be defined as an angle of deflection γof the ray L6. For example, if the ray L6 leaves the first lens arrayplate 24 perpendicularly to the plate, the angle of deflection γ=0°. Ifthe ray L6 leaves the first lens array plate 24 parallel to the plate,the angle of deflection γ=90°. If the ray L6 is reflectedperpendicularly to the first lens array plate 24, the angle ofdeflection γ=180°. It will be assumed here that the refractive index ofthe first lens array plate 24 is 1.53. In this case, the critical angleθc of the slope of the V groove 40 will be 40.8°.

FIG. 10 shows an optical path occurring when the angle of inclination εof the slope of the V groove in the second surface is equal to or lessthan the critical angle θc. In this case, the ray L6 incident on theslope of the V groove 40 is refracted by the slope of the V groove 40and is directed toward the second lens array plate, as shown in FIG. 10.

FIG. 11 shows an optical path occurring when the angle of inclination εof the slope of the V groove in the second surface is more than thecritical angle θc. FIG. 11 shows an optical path occurring when theangle of inclination ε=45°. In this case, the ray L6 totally reflectedby the slope of the V groove 40 is totally reflected again by the slopeof the adjacent V groove 40 before being directed toward the firstsurface (angle of deflection γ=180°. The optical path of FIG. 11 resultsbecause the angle of inclination ε=45°. The optical path of the ray L6totally reflected by the slope of the V groove 40 varies depending onthe value of the angle of inclination ε. For example, if the angle ofinclination ε=70°, the ray L6 totally reflected by the slope of a givenV groove 40 is refracted by the slope of the adjacent V groove 40 beforebeing directed to the second lens array plate.

FIG. 12 shows a relationship between the angle of inclination ε of theslope of the V groove in the second surface and the angle of raydeflection γ. As described with reference to FIG. 8, ghost noise is moresuccessfully reduced if the ray L6 is reflected toward the first surface(i.e., if the angle of deflection≧90°. Ghost noise is most successfullyreduced when the angle of deflection γ=180°. Therefore, it is mostdesirable to ensure that the angle of inclination ε of the V groove 40is 45°. As shown in FIG. 12, the angle of deflection γ varies dependingon the value of the angle of inclination ε. The range of the angle ofdeflection γ effective to reduce ghost noise varies depending on thelens design. Therefore, the angle of inclination ε may be appropriatelydetermined in accordance with the lens design.

FIG. 13 shows a relationship between the angle of inclination ε of theslope of the V groove in the third surface and the angle of raydeflection γ. In this case, the ray enters the second lens array platevia air so that the ray is not totally reflected. As shown in FIG. 13,as the angle of inclination ε of the slope of the V groove in the thirdsurface is increased, the angle of deflection γ is also increased. Inthe case of the V groove in the third surface, too, the range of theangle of deflection γ effective to reduce ghost noise varies dependingon the lens design. Therefore, the angle of inclination ε may beappropriately determined in accordance with the lens design.

FIGS. 9-13 depict cases where the angle of inclination of one of theslopes of the V groove is equal to the angle of inclination of the otherslope. However, one of the slopes of the V groove need not be equal tothe other slope. For example, one of the slopes of the V groove maydiffer from the other slope in the angle of inclination, depending onthe position of the V groove. Further, the angle of inclination of the Vgrooves may not be uniform. The angle may differ depending on theposition of the V groove. By adjusting the angle of inclinationappropriately depending on the position where the V groove is located,ghost noise is more suitably reduced.

In the erecting equal-magnification lens array plate 11 shown in FIG. 3,the second surface 24 d is formed with the V grooves 40. However, boththe second surface and the third surface may be formed with V grooves.In this case, the stray light is deflected at both the second and thirdsurfaces so that ghost noise is more successfully reduced. In this case,however, the width W1 of the V groove in the sub-scanning direction isdesirably equal to the aperture size D1 of the first lens 24 a. This isbecause the V grooves in the second surface 24 d and/or the thirdsurface 26 c might create additional ghost.

In the embodiment of FIG. 3, the first surface light-shielding member 30is a member of a film form, and the fourth surface light-shieldingmember 32 is a member of a plate form. Alternatively, both the firstsurface light-shielding member 30 and the fourth surface light-shieldingmember 32 may be a member of a plate form. By increasing the height ofthe light-shielding member thus, ghost noise is more successfullyreduced. Still alternatively, the first surface light-shielding member30 may be a member of a plate form, and the fourth surfacelight-shielding member 32 may be a member of a film form. Stillalternatively, the first surface through hole 30 a of the first surfacelight-shielding member 30 may be formed as a circular truncated cone. Inother words, the diameter of the opening of the first surface throughhole 30 a facing the document and that of the opening at the firstsurface may be different. Still alternatively, the fourth surfacethrough hole 32 a of the fourth surface light-shielding member 32 may beformed as a circular truncated cone. In other words, the diameter of theopening of the fourth surface through hole 32 a facing the image planeand that of the opening at the fourth surface may be different.

FIG. 14 shows an erecting equal-magnification lens array plate 1611according to a second alternative embodiment of the present invention.Further, the intermediate through hole 34 a of the intermediatelight-shielding member 34 in the erecting equal-magnification lens arrayplate 1611 of the second alternative embodiment is formed as a circulartruncated cone such that the hole diameter is progressively larger in aninversely tapered fashion away from the second surface 24 d toward thethird surface 26 c. In the second alternative embodiment, a plurality ofV grooves 42 are formed in the third surface inter-lens area 26 f of thethird surface 26 c, which is an inter-lens area located on the sidewhere the hole diameter of the intermediate through hole 34 a is larger.The second surface inter-lens area of the second surface 24 d is formedas a flat surface. In the erecting equal-magnification lens array plate1611, the first surface light-shielding member 30 is a member of a plateform and the fourth surface light-shielding member is removed.

As in FIG. 6, FIG. 14 shows optical paths of the ray L4 (broken line)and the ray L5 (chain line). In the erecting equal-magnification lensarray plate 1611 according to the second alternative embodiment, therays L4 and L5 are deflected in the sub-scanning direction of theerecting equal-magnification lens array plate 1611 by the V grooves 42formed in the third surface inter-lens area 26 f, as shown in FIG. 14.The rays L4 and L5 deflected by the V grooves 42 travel away from thelinear image sensor 20 after passing through the second lens array plate26 and so are not incident on the linear image sensor 20. Therefore, byusing the erecting equal-magnification lens array plate 1611 accordingto the second alternative embodiment, an erect equal-magnification imagein which ghost noise is reduced can be formed without providing thefourth surface light-shielding member. Consequently, the number ofcomponents is reduced so that the erecting equal-magnification lensarray plate can be implemented at a reduced cost.

In this embodiment, too, if the intermediate light-shielding member 34is displaced from where it should be during manufacturing, the secondsurface inter-lens area of the second surface 24 d, where no V groovesare provided, is not completely covered by the intermediatelight-shielding member 34, exposing a flat surface. This might createghost noise. For this reason, it is desirable that the V grooves beformed both in the second surface 24 d and the third surface 26 c.

In the erecting equal-magnification lens array plate 1611 shown in FIG.14, the first surface light-shielding member 30 cannot be removed. Inthe erecting equal-magnification lens array plate 11 shown in FIG. 3,the first surface light-shielding member 30 cannot be removed. Unlikethe linear image sensor 20, the document G has a large extent in thesub-scanning direction. Therefore, there are a plurality of paths forstray light traveling from the document G to the linear image sensor 20so that stray light cannot be successfully prevented from entering thelinear image sensor 20 merely by providing V grooves.

In the embodiment described above, it is assumed that the smaller of thediameters of the openings of the intermediate through hole 34 a is equalto the lens diameter. For example, in the embodiment shown in FIG. 2,the diameter of the opening of the intermediate light-shielding throughhole 34 a at the third surface is equal to the lens diameter of thethird lens 26 a. This ensures that the third surface inter-lens area 26f is completely covered by the intermediate light-shielding member 34.In this structure, however, not much margin of error is allowed forassembling the third lenses 26 a and the intermediate light-shieldingmember 34 with the result that the ease of assembly is impaired. Forthis reason, the smaller of the diameters of the openings of theintermediate through hole 34 a may be slightly more than the lensdiameter for the purpose of improving ease of assembly. In this case, asurface not covered by the intermediate light-shielding member 34 iscreated in both the second surface inter-lens area 24 f and the thirdsurface inter-lens area 26 f. Ghost noise will be more efficientlyremoved by forming V grooves in both the second surface 24 d and thethird surface 26 c.

In the embodiments described above, the intermediate light-shieldingmember 34 provided with the intermediate through hole 34 a formed as acircular truncated cone is used. Where the requirement for removingflare noise is not so severe, the intermediate light-shielding memberprovided with a cylindrical intermediate through hole may be used. Inthis case, too, the diameter of the opening of the intermediatelight-shielding through hole may be more than the lens diameter in orderto avoid impairing the ease of assembly. In this case, ghost noise isremoved to a certain extent by forming V grooves in either the secondsurface 24 d or the third surface 26 c. However, this creates a surfacenot covered by the intermediate light-shielding member 34 in both thesecond surface inter-lens area 24 f and the third surface inter-lensarea 26 f. Therefore, ghost noise is more efficiently removed by formingV grooves in both the second surface 24 d and the third surface 26 c.

A description will now be given of exemplary embodiments of the presentinvention. A simulation of noise ratio was conducted in an exemplaryembodiment and a comparative exemplary embodiment of the presentinvention. More specifically, a ray tracing simulation was conducted.The entirety of the erecting equal-magnification lens array plate isilluminated in the main scanning direction by a 90° Lambertian emissionfrom a point light source. The amount of imaging light arriving at aspecified point on the image plane is designated as the amount ofimaging light transmitted. The amount of light arriving elsewhere isdesignated as the amount of light transmitted as noise. The illuminationand calculation of the amount of light are conducted on a line extendingin the main scanning direction. A noise ratio is defined as a sum of theamount of light transmitted as noise divided by a sum of the amount ofimaging light transmitted.

FIG. 15 shows an erecting equal-magnification lens array plate 1711according to the exemplary embodiment of the present invention. As shownin FIG. 15, the erecting equal-magnification lens array plate 1711 isconfigured such that the second surface inter-lens area 24 f is formedwith a plurality of V grooves 40. The erecting equal-magnification lensarray plate 1711 is configured such that the first surfacelight-shielding member 30, the fourth surface light-shielding member 32,and the intermediate light-shielding member 34 of a plate form areprovided. The first surface through hole 30 a, the fourth surfacethrough hole 32 a, and the intermediate through hole 34 a are formed asa circular truncated cone. The erecting equal-magnification lens arrayplate according to the comparative exemplary embodiment differs from theexemplary embodiment in that a flat surface, instead of the V grooves40, is formed in the second surface inter-lens area 24 f.

The conditions for simulation common to the exemplary embodiment and thecomparative exemplary embodiment are such that the conjugation lengthTC=9.9 mm, the thickness of the first and second lens array plates 24and 26 (hereinafter, lens thickness)=1.05 mm, the pitch of arrangementof the first through fourth lenses (hereinafter, lens arrangementpitch)=0.7 mm, the lens diameter of the first lenses 24 a=0.6 mm, thelens diameter of the second lenses 24 b=0.4 mm, the lens diameter of thethird lenses 26 a=0.4 mm, the lens diameter of the fourth lenses 26b=0.6 mm, the gap between the first lens array plate 24 and the secondlens array plate 26 (hereinafter, gap)=0.8 mm, the refractive index ofthe first and second lens array plates 24 and 26=1.53, the height of thefirst surface light-shielding member 30=0.7 mm, the height of the fourthsurface light-shielding member 32=0.7 mm, the height of the intermediatelight-shielding member 34=0.80 mm, the diameter of the opening of thefirst surface through hole 30 a facing the document=0.45 mm, thediameter of the opening of the first surface through hole 30 a at thefirst surface=0.51 mm, the diameter of the opening of the fourth surfacethrough hole 32 a facing the image plane=0.45 mm, the diameter of theopening of the fourth surface through hole 32 a at the fourthsurface=0.51 mm, the diameter of the opening of the intermediate throughhole 34 a at the second surface=0.65 mm, and the diameter of the openingof the intermediate through hole 34 a at the third surface=0.35 mm.

FIG. 16 shows a result of simulation in the comparative exemplaryembodiment and the exemplary embodiment. The shape of the V grooves ofthe exemplary embodiments is varied as in (1)-(4) below. The noise ratiois computed in the case where the total width of the V grooves in thesub-scanning direction W1=0.51 mm and in the case where W1=200 mm.

(1) V groove width=5 μm, angle of inclination ε=60°, V groove height=4.3μm(2) V groove width=5 μm, angle of inclination ε=45°, V groove height=2.5μm(3) V groove width=10 μm, angle of inclination ε=60°, V grooveheight=8.7 μm(4) V groove width=10 μm, angle of inclination ε=45°, V grooveheight=5.0 μm

The simulation result in the comparative exemplary embodiment shows thatthe noise ratio is 1.07% both when the total width of the V grooves inthe sub-scanning direction W1=0.51 mm and when W1=200 mm. The simulationresult in the exemplary embodiment shows that the noise ratio is reducedin all cases of (1)-(4) in comparison to the comparative exemplaryembodiment, both when the total width of the V grooves in thesub-scanning direction W1=0.51 mm and when W1=200 mm. In particular, thenoise ratio is 0.38% in (1) and (3), demonstrating that the ratio isreduced to about ⅓ in comparison to the comparative exemplaryembodiment. The simulation result shows that the plurality of V groovesformed in the second surface inter-lens area are useful to furtherreduce ghost noise.

FIG. 17 shows an image writing device 200 according to anotherembodiment of the present invention. As shown in FIG. 17, the imagewriting device 200 comprises an LED array 206 comprising an array of aplurality of LED's, a substrate 204 on which the LED array 206 ismounted, a control unit 202 configured to control the LED array 206, theaforementioned erecting equal-magnification lens array plate 11 forcondensing light emitted from the LED array 206, a photosensitive drum208 for receiving the light transmitted through the erectingequal-magnification lens array plate 11, and a housing 210 foraccommodating the components. In FIG. 17, the developer device, thetransferring device, etc. provided around the photosensitive drum 208are omitted from the illustration. The explanation given above of theimage reading device 100 also applies to the image writing device byreplacing the document G of the image reading device 100 shown in FIG. 1by the photosensitive drum 208 in the image writing device 200 andfurther replacing the linear image sensor 20 of the image reading device100 by the LED array 206 in the image writing device 200.

The image writing device 200 is provided with an LED print head whichuses LED's as light sources. When an LED print head is used, pixelscorrespond one to one to light-emitting sources so that no mechanismsfor scanning are necessary. Therefore, the size and weight of the devicecan be reduced as compared with a laser raster output scanner (ROS)system in which a laser light source and a polygon mirror are combined.

In the related art, a rod lens array is used as an erectingequal-magnification lens array plate in a device in which an LED printhead is used. By using the erecting equal-magnification lens array plate11 according to the present invention, the cost of the image writingdevice 200 can be reduced. By using the erecting equal-magnificationlens array plate 11 according to the present invention, a high-qualityimage in which flare noise is reduced can be formed on thephotosensitive drum 208.

Described above is an explanation based on an exemplary embodiment. Theembodiment is intended to be illustrative only and it will be obvious tothose skilled in the art that various modifications to constitutingelements and processes could be developed and that such modificationsare also within the scope of the present invention.

In the embodiment described, lenses on the respective lens surfaces arearranged in a single row in the main scanning direction. Alternatively,lenses may be arranged in two or more rows in the main scanningdirection or arranged in a square array to reduce ghost noise equally.

1. An erecting equal-magnification lens array plate comprising: a firstlens array plate provided with a plurality of first lensessystematically arranged on a first surface and a plurality of secondlenses systematically arranged on a second surface opposite to the firstsurface; and a second lens array plate provided with a plurality ofthird lenses systematically arranged on a third surface and a pluralityof fourth lenses systematically arranged on a fourth surface opposite tothe third surface, wherein the first lens array plate and the secondlens array plate form a stack such that the second surface and the thirdsurface face each other to ensure that a combination of the lensesaligned with each other form a coaxial lens system, and an erectequal-magnification image of an object on the first surface side isformed on an image plane facing the fourth surface, the erectingequal-magnification lens array plate further comprising an intermediatelight-shielding member provided with a plurality of intermediate throughholes corresponding to the second and third lenses and provided betweenthe first lens array plate and the second lens array plate such that theintermediate through holes are located directly opposite to thecorresponding second and third lenses, and a plurality of V grooves areformed in an area between adjacent second lenses on the second surfaceand/or an area between adjacent third lenses on the third surface. 2.The erecting equal-magnification lens array plate according to claim 1,wherein the V grooves are formed to extend substantially parallel to themain scanning direction of the erecting equal-magnification lens arrayplate.
 3. The erecting equal-magnification lens array plate according toclaim 1, wherein the total width of the V grooves in the sub-scanningdirection is equal to or more than an aperture size of the first lenses.4. The erecting equal-magnification lens array plate according to claim1, wherein the adjacent V grooves are contiguous with each other attheir ends in the sub-scanning direction.
 5. An erectingequal-magnification lens array plate comprising: a first lens arrayplate provided with a plurality of first lenses systematically arrangedon a first surface and a plurality of second lenses systematicallyarranged on a second surface opposite to the first surface; and a secondlens array plate provided with a plurality of third lensessystematically arranged on a third surface and a plurality of fourthlenses systematically arranged on a fourth surface opposite to the thirdsurface, wherein the first lens array plate and the second lens arrayplate form a stack such that the second surface and the third surfaceface each other to ensure that a combination of the lenses aligned witheach other form a coaxial lens system, and an erect equal-magnificationimage of an object on the first surface side is formed on an image planefacing the fourth surface, the erecting equal-magnification lens arrayplate further comprising an intermediate light-shielding member providedwith a plurality of intermediate through holes corresponding to thesecond and third lenses and provided between the first lens array plateand the second lens array plate such that the intermediate through holesare located directly opposite to the corresponding second and thirdlenses, wherein the intermediate through hole is formed such that thehole diameter is progressively smaller in a tapered fashion away fromthe second surface toward the third surface, and a plurality of Vgrooves are formed in an area between adjacent second lenses on thesecond surface.
 6. The erecting equal-magnification lens array plateaccording to claim 5, wherein the V grooves are formed to extendsubstantially parallel to the main scanning direction of the erectingequal-magnification lens array plate.
 7. The erectingequal-magnification lens array plate according to claim 5, wherein thetotal width of the V grooves in the sub-scanning direction is equal toor more than an aperture size of the first lenses.
 8. The erectingequal-magnification lens array plate according to claim 5, wherein theadjacent V grooves are contiguous with each other at their ends in thesub-scanning direction.
 9. An erecting equal-magnification lens arrayplate comprising: a first lens array plate provided with a plurality offirst lenses systematically arranged on a first surface and a pluralityof second lenses systematically arranged on a second surface opposite tothe first surface; and a second lens array plate provided with aplurality of third lenses systematically arranged on a third surface anda plurality of fourth lenses systematically arranged on a fourth surfaceopposite to the third surface, wherein the first lens array plate andthe second lens array plate form a stack such that the second surfaceand the third surface face each other to ensure that a combination ofthe lenses aligned with each other form a coaxial lens system, and anerect equal-magnification image of an object on the first surface sideis formed on an image plane facing the fourth surface, the erectingequal-magnification lens array plate further comprising an intermediatelight-shielding member provided with a plurality of intermediate throughholes corresponding to the second and third lenses and provided betweenthe first lens array plate and the second lens array plate such that theintermediate through holes are located directly opposite to thecorresponding second and third lenses, wherein the intermediate throughhole is formed such that the hole diameter is progressively larger in aninversely tapered fashion away from the second surface toward the thirdsurface, and a plurality of V grooves are formed in an area betweenadjacent third lenses on the third surface.
 10. The erectingequal-magnification lens array plate according to claim 9, wherein the Vgrooves are formed to extend substantially parallel to the main scanningdirection of the erecting equal-magnification lens array plate.
 11. Theerecting equal-magnification lens array plate according to claim 9,wherein the total width of the V grooves in the sub-scanning directionis equal to or more than an aperture size of the first lenses.
 12. Theerecting equal-magnification lens array plate according to claim 9,wherein the adjacent V grooves are contiguous with each other at theirends in the sub-scanning direction.
 13. An optical scanning unitcomprising: a linear light source configured to illuminate an originalto be read; the erecting equal-magnification lens array plate accordingto claim 1 configured to condense light reflected by the original to beread; and a linear image sensor configured to receive light transmittedby the erecting equal-magnification lens array plate.
 14. An imagereading device comprising: the optical scanning unit according to claim13; and an image processing unit configured to process an image signaldetected by the optical scanning unit.
 15. An image writing devicecomprising: an LED array comprising an array of a plurality of LED's;the erecting equal-magnification lens array plate according to claim 1for condensing light emitted from the LED array; and a photosensitivedrum for receiving the light transmitted through the erectingequal-magnification lens array plate.
 16. An optical scanning unitcomprising: a linear light source configured to illuminate an originalto be read; the erecting equal-magnification lens array plate accordingto claim 5 configured to condense light reflected by the original to beread; and a linear image sensor configured to receive light transmittedby the erecting equal-magnification lens array plate.
 17. An imagereading device comprising: the optical scanning unit according to claim16; and an image processing unit configured to process an image signaldetected by the optical scanning unit.
 18. An image writing devicecomprising: an LED array comprising an array of a plurality of LED's;the erecting equal-magnification lens array plate according to claim 5for condensing light emitted from the LED array; and a photosensitivedrum for receiving the light transmitted through the erectingequal-magnification lens array plate.
 19. An optical scanning unitcomprising: a linear light source configured to illuminate an originalto be read; the erecting equal-magnification lens array plate accordingto claim 9 configured to condense light reflected by the original to beread; and a linear image sensor configured to receive light transmittedby the erecting equal-magnification lens array plate.
 20. An imagereading device comprising: the optical scanning unit according to claim19; and an image processing unit configured to process an image signaldetected by the optical scanning unit.
 21. An image writing devicecomprising: an LED array comprising an array of a plurality of LED's;the erecting equal-magnification lens array plate according to claim 9for condensing light emitted from the LED array; and a photosensitivedrum for receiving the light transmitted through the erectingequal-magnification lens array plate.